4 - 20 mA signal from a flow rate sensor

Hello,

I'm trying to work out on paper how I could accomplish a certain task using simple circuits that I could make myself.

What I'm trying to do is take a 4 - 20 mA signal from a flow rate sensor, convert that into a voltage corresponding to a certain flowrate, then run that voltage through a circuit which will integrate and give me a new voltage corresponding to a volume based on how long the voltage was read for. Is this possible, and if so how would the circuit look and would it be easy to make.

If I could get this circuit I would then run that output voltage which corresonds to a volume to a liquid level gauge calibrated to read certain voltages to show full or empty or somewhere in between.

The reason I can't just use a liquid level sensor is because I want to measure the volume going into a bladder, so floats won't work.

If this is possible is this the best way to do it, or would it be easier to run the 4 - 20 mA signal straight through a circuit that could integrate the current over time and then take that to the gauge.

Thanks for any advice in advance.

Circuit Design Question

Is your current always positive? If so you will saturate the integrator at some point...

I would convert the current into a voltage (with just a resistor, of course), use an ADC and do the integration in digital domain.

Re: Circuit Design Question

I think the best way to do this is convert to a voltage like Joannes said. Depending on your set up, you could run this current through a resistor to ground. If you use a resistor of 10 Ohms, you would get a voltage from 40mV to 200mV.

If you are worried about the op amp integrator saturating too soon, use a smaller resistor (this depends on your op amp voltage, if you have it higher, the less chance of saturation). Also, to get accurate results after each measurement, you should empty the integrator by shorting the capacitor briefly in between measurements.

This is one option. Hope it helps

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Justin
TheModernEngineer.blogspot.com